The present application relates generally to portable heater assemblies, particularly to heater assemblies housing fans, igniters, and heating devices in which a highly efficient catalytic combustion apparatus is employed to generate heat from a vaporous fuel with reduced toxic emissions.
Heater assemblies are well known in the art. A typical heater assembly may house a source of heat, i.e., a heating device, a power source or a connection to a power source, a fan and a control device. An electrical heater, for example, may include electrical heating elements, an electrical cord, an electrical fan and a power switch. After connecting the electrical cord to a wall outlet, engaging the power switch may activate the electrical fan and the electrical heating elements. The fan may force air past the heating elements, heating the air by convection.
However, use of more complicated heating devices similarly complicates the assembly of the heater. Use of a catalytic combustion apparatus, for example, requires special considerations when designing a heater assembly. A portable catalytic combustion apparatus using a portable fuel source would be a desirable alternative to an electric heater when portability and freedom of movement are necessary. For example, an electric heater would be undesirable when an ample electric power source is not readily available, as may be the case when camping.
A typical catalytic combustion apparatus oxidizes a gaseous fuel, such as methane, butane or propane, at room temperature to generate heat. Generally, the fuel is introduced into a gas-tight housing where the fuel expands to completely fill the housing. As the fuel diffuses through a catalyst-containing substrate located at an outlet of the housing, ambient air mixes with the diffused fuel. The fuel-air mixture is then oxidized by a reaction promoted by the catalyst to produce heat. Such catalysts typically include noble metals such as platinum group metals or compounds containing the same. The substrates upon which the catalysts are supported are typically made from glass fibers, porous metals or ceramics such as ceramic wool or ceramic board and the like.
The products of the catalyst-enhanced oxidation reaction, such as carbon dioxide and water vapor, are discharged through the outside surface of the catalyst-containing substrate. Convection currents disperse the reaction products and draw in ambient air to provide oxygen to sustain the reaction. Igniting the reactants normally starts the reaction. Ignition usually requires a flame (e.g., a pilot light) or a spark, which may be induced, for example, by an electrical ignition.
A drawback of such known combustion apparatuses is reliance on convection currents to circulate the reactants (air and fuel) and to remove combustion products from the catalyst-containing reaction zone. A factor which contributes to controlling the rate of oxygen available per unit area of catalyst is the rate of convection flow over the active catalytic surface. Convection currents often produce irregular and erratic flows of reactants over the active catalytic surface. Under such conditions, there is typically an uneven distribution of oxygen and/or fuel within the reaction zone containing the catalyst. Consequently, when oxygen is available in less than a stoichiometric amount relative to the fuel, incomplete combustion of the fuel occurs resulting in harmful by-products including carbon monoxide, unburned fuel and the like. As carbon monoxide and unreacted fuel accumulate, a dangerous health hazard arises that could result in serious injury or death to occupants of an enclosed space in which the heating apparatus is used.
Consequently, a heater assembly using such a catalytic heating apparatus might encounter difficulties if a fan were blowing directly onto the heating element, in this case the catalyst-containing substrate. Air forced directly over the catalyst-containing element may unevenly distribute the fuel and oxygen, and it may cause unstoichiometric ratios of fuel to oxygen at the catalyst. Similarly, igniting the fuel at the catalyst with an open flame would be more difficult if air were being forced over catalyst.
The present application is directed generally to a portable heater assembly including an encasement, a fan, a battery pack, an igniter, power controls, and a heating apparatus with reduced toxic emissions. The heating apparatus may employ a highly efficient catalytic combustion apparatus to generate heat from a vaporous fuel. The heating apparatus may comprise a fuel source, an air inlet, a mixing device, and a catalyst-containing combustion chamber for generating heat. By virtue of being completely self-contained, an exemplary embodiment of the portable heating assembly may be moved easily and operated independently from outside power sources.
The air inlet may be in communication with the mixing device for creating a uniform fuel-air mixture with a desirable ratio of air to fuel before the fuel-air mixture is combusted in the catalyst-containing combustion chamber. Such pre-mixing of the fuel and air provides for a cleaner and more efficient heat generating combustion that results in substantially reduced emissions of toxic substances, such as carbon monoxide and unreacted fuel, and in an improved operating life of the apparatus.
In particular, one aspect of the present invention is directed to a heating apparatus that includes a combustion chamber having an inlet for receiving a uniform fuel-air mixture, and an outlet. The combustion chamber further includes a catalyst-containing substrate for initiating combustion of the fuel-air mixture. A fuel source and an air inlet are provided in communication with a mixing device for mixing the fuel and air under conditions which provide for a uniform fuel-air mixture, and for delivering the uniform fuel-air mixture through the inlet to the substrate in the combustion chamber to produce heat with minimal production of harmful by-products.
In an exemplary embodiment of the present invention, the encasement supports and encases the fan, the igniter, the power controls, the heating apparatus and the connection to the fuel source. The power controls include an electric switch, an ignition activator, and a fuel valve. The electric switch controls the fan by forming an electrical connection between a battery pack and the fan. The fuel valve regulates the flow of fuel, which in turn regulates whether heat is generated. The fan draws in outside air from around the encasement, and the encasement channels the forced air from the fan around the perimeter of the heating apparatus. Expelling the air around the perimeter of the heating apparatus avoids blowing the forced air directly at the catalyst-containing combustion chamber, which might interfere with the fuel-air mixture.